The field of the invention is major histocompatibility complex (MHC) antigens.
Major histocompatibility complex (MHC) class II antigens are cell surface receptors that orchestrate all specific immune responses in vertebrates. Humans possess three distinct MHC class II isotypes: DR, for which approximately 70 different allotypes are known; DQ, for which 33 different allotypes are known; and DP, for which 47 different allotypes are known. Each individual bears two to four DR alleles, two DQ alleles, and two DP alleles.
MHC receptors (both class I and class II) participate in the obligate first step of immune recognition by binding small protein fragments (peptides) derived from pathogens or other non-host sources, and presenting these peptides to the regulatory cells (T cells) of the immune system. In the absence of MHC presentation, T cells are incapable of recognizing pathogenic material. Cells that express MHC class II receptors are termed antigen presenting cells (APC). APCs ingest pathogenic organisms and other foreign materials by enveloping them in endosomic vesicles, then subjecting them to enzymatic and chemical degradation. Foreign proteins which are ingested by APCs are partially degraded or xe2x80x9cprocessedxe2x80x9d to yield a mixture of peptides, some of which are bound by MHC class II molecules that are en route to the surface. Once on the cell surface, MHC-bound peptides are available for T cell recognition.
MHC class II antigens are expressed on the surface of APCs as a trimolecular complex composed of an xcex1 chain, a p chain, and a processed peptide. Like most polypeptides that are expressed on the cell surface, both xcex1 and xcex2 chains contain short signal sequences at their NH2 termini which target them to the endoplasmic reticulum (ER). Within the ER the class II xcex1/xcex2 chain complex associates with an lo additional protein termed the invariant chain (Ii). Association with Ii is proposed to block the premature acquisition of peptides (by blocking the peptide binding cleft of the MHC heterodimer), promote stable xcex1/xcex2 interaction, and direct subsequent intracellular trafficking of the complex to endosomal vesicles. In the endosomes, Ii is removed by a process involving proteolysis; this exposes the peptide binding cleft, thus allowing peptides present in the endosome to bind to the MHC molecule. The class II/peptide complex is transported from the endosomes to the cell surface where it becomes accessible to T-cell recognition and subsequent activation of immune responses. Class II MHC molecules bind not only to peptides derived from exogenous (ingested) proteins, but also to those produced by degradation of endogenous (self) proteins. The amount of each species of peptide which binds class II is determined by its local concentration and its relative binding affinity for the given class II binding groove, with the various allotypes displaying different peptide-binding specificities.
Early during fetal development, the mammalian immune system is xe2x80x9ctolerizedxe2x80x9d, or taught not to react, to self-peptides. The stability and maintenance of this system is critical for ensuring that an animal does not generate an immune response against self. A breakdown of this system gives rise to autoimmune conditions such as diabetes, rheumatoid arthritis and multiple sclerosis. Current technologies intended to manipulate the immune system into reestablishing proper nonresponsiveness include protocols involving the intravenous delivery of synthetic, high affinity binding peptides as blocking peptides.
Vaccination can generate protective immunity against a pathogenic organism by stimulating an antibody-mediated and/or a T cell-mediated response. Most of the current vaccination strategies still use relatively crude preparations, such as attenuated or inactivated viruses. These vaccines often generate both antibody- and cell-mediated immunity, and do not allow one to modulate the type of immune response generated. Moreover, in many diseases the generation of the wrong type of response can result in an exacerbated disease state.
In the work disclosed herein, naturally processed peptides bound to six of the some 70 known human MHC class II DR allotypes (HLA-DR1, HLA-DR2, HLA-DR3, HLA-DR4, HLA-DR7, and HLA-DR8) have been characterized. These peptides were found to be predominantly derived from self proteins rather than foreign proteins. Several self peptide families have been identified with the unexpected property of degenerate binding: that is, a given self-peptide will bind to a number of HLA-DR allotypes. This observation runs counter to the widely-accepted view of MHC class II function, which dictates that each allotype binds a different set of peptides. Furthermore, many if not all of the self-peptides disclosed herein bind to the class II molecules with relatively high affinity. These three characteristicsxe2x80x94(1) self rather than foreign, (2) degeneracy, and (3) high affinity bindingxe2x80x94suggest a novel means for therapeutic intervention in disease conditions characterized by autoreactivity, such as Type I diabetes, rheumatoid arthritis, and multiple sclerosis. In addition, such therapy could be used to reduce transplant rejection.
In the therapeutic methods of the invention, short peptides modelled on the high-affinity immunomodulating self peptides of the invention (which preferably are nonallelically restricted) are introduced into the APCs of a patient. Tissue typing to determine the particular class II alleles expressed by the patient may be unnecessary, as the peptides of the invention are bound by multiple class II isotypes. It may be useful to employ a xe2x80x9ccocktailxe2x80x9d of peptides, where complete degeneracy is lacking for individual peptides, i.e., where peptides binds to fewer than all allotypes; the cocktail provides overlapping binding specificity. Once in the APC, a peptide binds to the class II molecules with high affinity, thereby blocking the binding of immunogenic peptides which are responsible for the immune reaction characteristic of the disease condition. Because the blocking peptides of the invention are self peptides with the exact carboxy and amino termini tolerized during ontogeny, they are immunologically inert and will not induce an immune response which may complicate treatment using non-self blocking peptides.
The peptides of the invention may be introduced into APCs directly, e.g., by intravenous injection of a solution containing one or more of the peptides. Alternatively, the APCs may be provided with a means of synthesizing large quantities of the blocking peptides intracellularly. Recombinant genes that encode ER and/or endosomal targeting signals fused to blocking peptide sequences are linked to appropriate expression control sequences and introduced into APCs. Once in the cell, these genes direct the expression of the hybrid peptides. Peptides targeted to the ER will bind class II xcex1 and xcex2 chains as they are translated and assembled into heterodimers. The presence of high affinity binding peptides within the ER will prevent association of the xcex1/xcex2 complex with invariant chain, and thus interfere with intracellular trafficking. The class II molecule/blocking peptide complex may subsequently be expressed on the cell surface, but would not elicit an immune response since T cells are tolerized to this complex early in development. The use of peptides tagged with ER retention signals may also prevent the peptide-complexed class II molecules from leaving the ER. Alternatively, the recombinant peptide may be tagged with an endosomal targeting signal which directs it to the endosomal compartment after synthesis, thereby also skewing the ratio of endogenously-processed peptide to blocking peptide in the endosome and favoring binding of the high affinity blocking peptide to any class II molecules which did not bind it in the ER. It may be advantageous, for any individual patient, to employ one or more ER-directed peptides in combination with one or more endosome-directed peptide, so that xcex1-xcex2 complexes which are not filled in the ER with peptides of the invention are then blocked in the endocytic pathway. The end result again is cell surface expression of a non-immunogenic class II/peptide complex.
The use of a class II nonrestricted high affinity binding peptide coupled to an intracellular delivery system permits the specific down-regulation of class II restricted immune responses without invoking the pleiotropic adverse reactions associated with the current pharmacological strategies. Successful application of these technologies will constitute a significant advance towards the treatment of autoimmune disease and prevention of transplant rejection.
The intracellular delivery system of the invention can also be utilized in a novel method of vaccination of an animal, e.g., a human patient or a commercially significant mammal such as a cow which is susceptible to diseases such as hoof and mouth disease. Such a system can be tailored to generate the type of immune response required in a given situation by adjustments in the following: (a) peptide specificity for class I or class II MHC; (b) peptide/protein length and/or sequence, and (c) using specific tags for organelle targeting. The system of the invention ensures that peptides are produced only within cells, and are not present outside the cells where they could stimulate antibody production by contact with B cells. This limits the immune response generated by such a vaccine to T cell-mediated immunity, thereby preventing either an inappropriate or potentially deleterious response as might be observed with standard vaccines targeting the organisms which cause, for example, HIV, malaria, leprosy, and leishmaniasis. Furthermore, this exclusively T cell-mediated immune response can be class I or class II-based, or both, depending upon the length and character of the immunogenic peptides: MHC class I molecules are known to bind preferentially to peptides 8 to 10 residues in length, while class II molecules bind with high affinity to peptides that range from 12 to 25 residues long.
Immunization and therapy according to the invention can employ a purified preparation of a peptide of the invention, i.e., a peptide which includes an amino acid sequence identical to that of a segment of a naturally-occurring human protein (i.e., a xe2x80x9cself proteinxe2x80x9d), such segment being of 10 to 30 residues in length, wherein the peptide binds to a human MHC class II allotype, and preferably binds to at least two distinct MHC class II allotypes (e.g., any of the approximately 70 known DR allotypes, approximately 47 known DP allotypes, or approximately 33 known DQ allotypes). The portion of the peptide corresponding to the self protein segment is herein termed a xe2x80x9cself peptidexe2x80x9d. By xe2x80x9cpurified preparationxe2x80x9d is meant a preparation at least 50% (by weight) of the polypeptide constituents of which consists of the peptide of the invention. In preferred embodiments, the peptide of the invention constitutes at least 60% (more preferably at least 80%) of the purified preparation. The naturally-occurring human protein is preferably HLA-A2 (as broadly defined below), HLA-A29, HLA-A30, HLA-B44, HLA-B51, HLA-Bw62, HLA-C, HLA-DP xcex2-chain, HLA-DQ xcex1-chain, HLA-DQ xcex2-chain, HLA-DQ3.2 xcex2-chain, HLA-DR xcex1-chain, HLA-DR xcex2-chain, HLA-DR4 xcex2-chain, invariant chain (Ii), Ig kappa chain, Ig kappa chain C region, Ig heavy chain, Na+/K+ ATPase, potassium channel protein, sodium channel protein, calcium release channel protein, complement C9, glucose-transport protein, CD35, CD45, CD75, vinculin, calgranulin B, kinase C xcex6-chain, integrin xcex2-4 gp150, hemoglobin, tubulin xcex1-1 chain, myosin xcex2-heavy chain, xcex1-enolase, transferrin, transferrin receptor, fibronectin receptor xcex1-chain, acetylcholine receptor, interleukin-8 receptor, interferon xcex1-receptor, interferon xcex3-receptor, calcitonin receptor, LAM (lymphocyte activation marker) Blast-1, LAR (leukocyte antigen-related) protein, LIF (leukemia inhibitory factor) receptor, 4F2 cell-surface antigen (a cell-surface antigen involved in normal and neoplastic growth) heavy chain, cystatin SN, VLA-4 (a cell surface heterodimer in the integrin superfamily of adhesion receptors), PAI-1 (plasminogen activator inhibitor-1), IP-30 (interferon-xcex3 induced protein), ICAM-2, carboxypeptidase E, thromboxane-A synthase, NADH-cytochrome-b5 reductase, c-myc transforming protein, K-ras transforming protein, MET kinase-related transforming protein, interferon-induced guanylate-binding protein, mannose-binding protein, apolipoprotein B-100, cathepsin C, cathepsin E, cathepsin S, Factor VIII, von Willebrand factor, metalloproteinase inhibitor 1 precursor, metalloproteinase inhibitor 2, plasminogen activator inhibitor-1, or heat shock cognate 71 kD protein; it may be an MHC class I or II antigen protein or any other human protein which occurs at the cell surface of APCs. The self peptide preferably conforms to the following motif: at a first reference position (I) at or within 12 residues of the amino terminal residue of the segment, a positively charged residue (i.e., Lys, Arg, or His) or a large hydrophobic residue (i.e., Phe, Trp, Leu, Ile, Met, Tyr, or Pro; and at position I+5, a hydrogen bond donor residue (i.e., Tyr, Asn, Gln, Cys, Asp, Glu, Arg, Ser, Trp, or Thr). In addition, the peptide may also be characterized as having, at positions I+9, I+1, and/or Ixe2x88x921, a hydrophobic residue (i.e., Phe, Trp, Leu, Ile, Met, Pro, Ala, Val, or Tyr) (+ denotes positions to the right, or toward the carboxy terminus, and xe2x88x92 denotes positions to the left, or toward the amino terminus.) A typical peptide of the invention will include a sequence corresponding to residues 32-41 (i.e., TQFVRFDSDA; SEQ ID NO: 149) or residues 107-116 (i.e., DWRFLRGYHQ; SEQ ID NO: 150) of HLA-2, or residues 108-117 (i.e., RMATPLLMQA; SEQ ID NO: 151) of Ii, or a sequence essentially identical to any one of the sequences set forth in Tables 1-10 below.
The therapeutic and immunization methods of the invention can also employ a nucleic acid molecule (RNA or DNA) encoding a peptide of the invention, but encoding less than all of the entire sequence of the self protein. The nucleic acid preferably encodes no substantial portion of the self protein other than the specified self peptide which binds to a MHC class II molecule, although it may optionally include a signal peptide or other trafficking sequence which was derived from the self protein (or from another protein). A trafficking sequence is an amino acid sequence which functions to control intracellular trafficking (directed movement from organelle to organelle or to the cell surface) of a polypeptide to which it is attached. Such trafficking sequences might traffic the polypeptide to ER, a lysosome, or an endosome, and include signal peptides (the amino terminal sequences which direct proteins into the ER during translation), ER retention peptides such as KDEL (SEQ ID NO: 152); and lysosome-targeting peptides such as KFERQ (SEQ ID NO: 153), QREFK (SEQ ID NO: 154), and other pentapeptides having Q flanked on one side by four residues selected from K, R, D, E, F, I, V, and L. An example of a signal peptide that is useful in the invention is a signal peptide substantially identical to that of an MHC subunit such as class II xcex1 or xcex2; e.g., the signal peptide of MHC class II xcex1 is contained in the sequence MAISGVPVLGFFIIAVLMSAQESWA (SEQ ID NO: 155). The signal peptide encoded by the nucleic acid of the invention may include only a portion (e.g., at least ten amino acid residues) of the specified 25 residue sequence, provided that portion is sufficient to cause trafficking of the polypeptide to the ER. In preferred embodiments, the nucleic acid of the invention encodes a second self peptide and a second trafficking sequence (which may be identical to or different than the first self peptide and first trafficking sequence), and it may encode additional self peptides and trafficking sequences as well. In still another variation on this aspect of the invention, the self peptide sequence (or a plurality of self peptide sequences arranged in tandem) is linked by a peptide bond to a substantially intact Ii polypeptide, which then carries the self peptide sequence along as it traffics the class II molecule from ER to endosome.
The nucleic acid of the invention may also contain expression control sequences (defined as transcription and translation start signals, promoters, and enhancers which permit and/or optimize expression of the coding sequence with which they are associated) and/or genomic nucleic acid of a phage or a virus, such as an attenuated or non-replicative, non-virulent form of vaccinia virus, adenovirus, Epstein-Barr virus, or a retrovirus.
The peptides and nucleic acids of the invention may be prepared for therapeutic use by suspending them directly in a pharmaceutically acceptable carrier, or by encapsulating them in liposomes, immune-stimulating complexes (ISCOMS), or the like. Such preparations are useful for inhibiting an immune response in a human patient, by contacting a plurality of the patient""s APCs with the therapeutic preparation and thereby introducing the peptide or nucleic acid into the APCS.
Also within the invention is a cell (e.g., a tissue culture cell or a cell, such as a B cell or APC, within a human) containing the nucleic acid molecule of the invention. A cultured cell containing the nucleic acid of the invention may be used to manufacture the peptide of the invention, in a method which involves culturing the cell under conditions permitting expression of the peptide from the nucleic acid molecule.
Disclosed herein is a method of identifying a nonallelically restricted immunomodulating peptide, which method includes the steps of:
(a) fractionating a mixture of peptides eluted from a first MHC class II allotype;
(b) identifying a self peptide from this mixture; and
(c) testing whether the self peptide binds to a second MHC class II allotype, such binding being an indication that the self peptide is a nonallelically restricted immunomodulating peptide.
In further embodiments, the invention includes a method of identifying a potential immunomodulating peptide, in a method including the steps of:
(a) providing a cell expressing MHC class II molecules on its surface;
(b) introducing into the cell a nucleic acid encoding a candidate peptide; and
(c) determining whether the proportion of class II molecules which are bound to the candidate peptide is increased in the presence of the nucleic acid compared to the proportion bound in the absence of the nucleic acid, such an increase being an indication that the candidate peptide is a potential immunomodulating peptide.
Also within the invention is a method of identifying a potential immunomodulating peptide, which method includes the steps of:
(a) providing a cell expressing MHC class II molecules on its surface;
(b) introducing into the cell a nucleic acid encoding a candidate peptide; and
(c) determining whether the level of MHC class II molecules on the surface of the cell is decreased in the presence of the nucleic acid compared to the level of MHC class II molecules in the absence of the nucleic acid, such a decrease being an indication that the candidate peptide is a potential immunomodulating peptide.
Also included in the invention is a method of identifying a nonallelically restricted immunostimulating peptide, which method includes the steps of:
(a) providing a cell bearing a first MHC class I or class II allotype, such cell being infected with a pathogen (e.g., an infective agent which causes human or animal disease, such as human immunodeficiency virus (HIV), hepatitis B virus, measles virus, rubella virus, influenza virus, rabies virus, Corynebacterium diphtheriae, Bordetella pertussis, Plasmodium spp., Schistosoma spp., Leishmania spp., Trypanasoma spp., or Mycobacterium lepre);
(b) eluting a mixture of peptides bound to the cell""s first MHC allotype;
(c) identifying a candidate peptide from the mixture, such candidate peptide being a fragment of a protein from the pathogen; and
(d) testing whether the candidate peptide binds to a second MHC allotype, such binding being an indication that the candidate peptide is a nonallelically restricted immunostimulating peptide. A nucleic acid encoding such an immunogenic fragment of a protein of a pathogen can be used in a method of inducing an immune response in a human patient, which method involves introducing the nucleic acid into an APC of the patient.
The therapeutic methods of the invention solve certain problems associated with prior art methods involving intravenous injection of synthetic peptides: (1) because of allelic specificity, a peptide capable of binding with high affinity to all, or even most, of the different class II allotypes expressed within the general population had not previously been identified; (2) the half-lives of peptides delivered intravenously are generally very low, necessitating repeated administration with the associated high level of inconvenience and cost; (3) this type of delivery approach requires that the blocking peptide displace the naturally-occurring peptide occupying the binding cleft of a class II molecule while the latter is on the cell surface, which is now believed to be a very inefficient process; and (4) if the blocking peptide utilized is itself immunogenic, it may promote deleterious immune responses in some patients.
Other features and advantages of the invention will be apparent from the following detailed description, and from the claims.